[ENHANCEMENT] Add pre-flight check in C8Run release workflow for Docker Compose dependency

[bkenez]

Overview

C8Run packages Docker Compose artifacts at build time by downloading them from camunda/camunda-distributions GitHub releases:

composeUrl := "https://github.com/camunda/camunda-distributions/releases/download/docker-compose-" + composeTag + "/docker-compose-" + composeTag + ".zip"

If a release manager triggers the C8Run release workflow before Docker Compose has been released, the build fails partway through after already consuming CI resources on 4 parallel runners (Ubuntu, macOS ARM, macOS Intel, Windows).

Proposal

Add a pre-flight check step at the start of the C8Run release workflow (camunda/camunda/.github/workflows/c8run-release.yaml) that verifies the required Docker Compose release exists before starting the multi-platform build matrix:

- name: Verify Docker Compose release exists
  run: |
    compose_version="${{ inputs.camundaVersion }}"
    gh release view "docker-compose-${compose_version}" \
      --repo camunda/camunda-distributions || \
      (echo "ERROR: Docker Compose release docker-compose-${compose_version} not found. Release Docker Compose first." && exit 1)

This would fail fast with a clear error message instead of failing 15+ minutes into the build.

Acceptance Criteria

• C8Run release workflow includes a pre-flight check for Docker Compose release existence
• The check runs before the build matrix starts
• Failure message clearly indicates the missing dependency and required action